Changeable resistance



June 25, 1929- H. R. VAN DEVENTER CHANGEABLE RESISTANCE Filed Jan. ll, 192A g. ff /147 Mk@ x aamlmllmu Patented June 25, 1929.

UNITED STATES 1,718,320 PATENT OFFICE.

HARRY R. VAN DEVENTER, F NEWV YORK, N. Y., ASSIGNOR TO DUBILIER CONDENSER CORPORATION, 0F NEW YORK, N. Y., A CORPORATION OF DELAWARE.

CHANGEABLE RESISTANCE.

Application led January 11, 1924. Serial No. 685,603.

My invention relates to resistances, and more particularly to variable .resistances capable of minute adjustment.

An object of my invention is to devise a variable resistance which is compact and sturdily built, and in which there may be minute adjustment of resistance values over a lar e area.

A urther object of my invention is to provide a structure having a variable resistance capable of minute adjust-ment, and having a condenser connected across the terminals of the resistance, thus comprising within a single structure a device capable of wide use in radio. systems.

Yet another object of my .invention is to provide a variableresistance in which the entire operative structure is comprised within a casing, upon the outside of which is visually indicated the adjustment and resistance under all conditions.

Still another object of my invention is' to provide a structure in which the movement of the parts to effect changes in resistance is accomplished with a minimum of friction or strain on the moving parts.

With these and other objects in view, which may be incident to my improvements, the intions to be hereinafter set forth and claimed, with the understanding that the several necessary elements comprising my invention, may be varied in construction, proportions an arrangement, without departing from the spirit and scope of the appended claims.

In order to make my invention more clearly understood, I have shown in the accompanyingdrawings means for carryin the same into practical effect, without limiting the improvements in their useful applications to the particular constructions, which for the purpose of explanation, have been made the subject of illustration.

In the drawings:

Figure 1 is a top plan view of my variable resistance;

Fig. 2 is a bottom plan view ofthe device with vthe bottom casing removed;

Fig. 3 is a cross sectional view taken through the axisl of rotation of the'device, and on the line 3 3 of Fig. 1, looking in the direction of the arrows;

Fi 4 is a view partl in cross section, taken on t e line 4-4 of` ig. f1, looking in the direction of the arrows;

vention consists in the parts and combina-` connected to binding posts which project from the casing. A short-circuiting resilient metallic strip 'is fixed to the stationary resistor at one of its terminals, and is of curved configuration conforming to the curve'of the fixed resistor. This flexible metallic stripis intentioned awa from the fixed resistor and does not normally contact therewith except at its fixed end. A shaft having an operating knob on the exterior of the casing has an end projecting into the interior of the casing, and an arm having a presser foot on its end is adapted to be rotated by the shaft so that the presser foot shall bear against the sul face of the flexible resistor elementrand cause it to bear against the adjacent surface of the fixed resistor. By rotating the shaft and moving the arm` the presser foot will cause the fixed resistor to be short-circuited by varying portions of the metallic strip and the resistance of the device will be changed. A condenser is shunted across the binding posts of the fixed resistor. On the exterior of the 90 casing are indicia which give the setting of f the resistance in cooperation with a movable pointer turning with the knob that revolves the shaft. The pointer preferably coincides with the position of the arm carrying the presserfoot. Y

Referrin more particularly to the draw- 'ings for a etailed description, I have shown an insulating casing 1 having a downwardly depending annular wall 2 provided on its 100 interior with a shoulder 3. On the shoulder 3 rests a bottom cover plate 4 also of insulating material. On the interior of the casing and against the lower surface of the upper wall of the casing 1 is mounted a strip 5 of 105 resistance material. which inthe present instance may comprise a strip of cardboard whose upper surface is covered with carbon. The covering of carbon on the strip 5 I have designated by the numeral 6. The strip 5 11o Cil is of arcuate shape, and in the present instance comprises about three-fourths of a circle. The strip 5 terminates in offset portions 7 which project in a radial direction. Pass-l ing through the offset portions 7 are binding post screws 8 and 9.

A condenser 11 is shunted across the terminals 7 of the fixed resistance element 5.

The condenser comprises an inner foil member 12, through the free end of which passes the binding post 9. r[he foil member 12 is covered by sheets of mica 13 on either side. Wrapped around the sheets vofmica 13 is a metallic holding ewrapper 14 which comprises the other plate ofthe condenser. The metallic holding wrapper 14 has an overlapping end 15 which, when pressed down, holds the. condenser compactly together. The holding wrapper 14 has a projecting tab 16 through which the binding post 8 passes. Mounted over the foil condenser member 12 is a metallic washer 17. On the portion of the binding post screw 9 projecting upwardly through the casing is screwed a nut 18 which, whenA tightened, pulls the washer 17 toward the upper interior wall of the casing and causes good electrical contact to be made between the carbon surface 6 of the fixed resistor, the interior element 12 ofthe condenser 11, and the binding post screw 9. A metallic knurled knob 19 is screwed on the portion of the binding post 9 that projects beyond the nut 18, and a wire can be held between the nut 18 and the knob when the knob is screwed in place. f

v'Positioned between the tab 16 of the outer member 14 of the condenser 11 and the conducting surface 6 of the fixed resistor is a resilient metallic condenser element 21. The metallic condenser element. 21 has one free end 22, and is of a shape conforming to the shape of the fixed element 5 of my variable condenser. The resilient spring element 21 is intentioned away from the fixed element 5, as is plainly seen in Fig. 4. The portion of the binding post screw 8 projecting through the upper wall of the container 1 has screwed thereon a nut 23, and a knurled metallic knob 24vis adapted to be screwed on over the nut tohold they wire leading to that terminal of my variable condenser.

Passing through the upper wall of the insulating container 1, through an aperture therein, is a metallic sha-ft 25, which is journaled in the aperture in that wall. The shaft 25 is provided at its lower extremitywith a shoulder 26, and from the shoulder 26 projects downwardly a depending flange 27.

Adapted to fit over the depending flange 27 is a lflat metallic piece or arm.` 28 of spring metal, provided with an aperture through which the downwardly dependngan'ge 27 passes. After placing the arm 28'over the fiange 27, the fiange 27 is riveted, as shown, at 29, to hold the arm 28 in position. The

arm 28 is provided at its outer extremity, which is approximately the same distance from the axis of rotation of the shaft as are the fiexible and movable elements of my condenser, with an aperture 31 through which passes the downwardly projecting shank 32 of a presser foot or button 33. The shank 32 fits loosely in the aperture 31 so that the presser foot 33 can rotate on the shank 32 as an axis.

Mounted on the shaft 25, and located just above the spring arm 28, is a metallic washer 34. The arm 28 is provided with a bend 35 therein, which permits the arm to readily pass over the washe`r34 without undue friction, and at the same time permits the outer end 36 of the arm 28 to be angularly disposed to the under surface of the upper wall of the container 1. This causes the presser foot. 33 to have its surface disposed at an angle to the surface of both the fixed and movable flexible resilient elements of my variable condenser.

Such constructi-on, wherein the presser foot is disposed at an angle to the horizont-al, insures that the presser foot will bear against. the surface of the resilient movable element 21 of the condenser with an equal pressure, and, therefore, in making the adjustments, when the presser foot-slides over the surface of the flexible movable element 21 to press it down into contact with the fixed element to shortcircuit a portion of the fixed element, the presser foot will be given a mo-V tion of rotation which will facilitate the movement of the arm 28 and eliminate to a large degree the friction of adjustment. The presser foot is preferably of insulating material, such as bakelite or rubberoid.

Passing through the axis of the shaft 25 is an assembly screw 37. Passing around the shaft. 25 is a washer 38 which has integrally formed therewith a pointer 39. An insulat-A ing operating knob 41 has an aperture 42 in its head in which the screw-head 43 of the screw 37 fits. By screwing up the screw 37, the knob 41 compresses the washer member 38 against the upper surface of the container 1. vUpon movement of the operating knob 41, the shaft 25 will be rotated and the pointer 39 integrally formed with the washer 38 will move. The ,apparatus is assembled so that the pointer 39 will lie adjacent the arm 28, and the pointJ of adjustment of the arm 28 will be indicated by the position of the pointer 39. The pointer 39 cooperates with a scale 44 stamped on the upper surface of the upper wall of the casing 1. Stop lugs 45 and 46 prevent the movement of the operating arm 28 beyond certain definite positions, by reason of the fact that the pointer 39 contacts with the stops 45 and 46 in the maximum and the minimum adjustments of the condenser.

Preferably integrally formed with the casing 1, and on the lnterior walls of the downwardly projecting flange 2, are inwardly projecting supports 47. Other inwardly projectin supports 48 of a trifle larger size are provi ed with holes 49 therein through which screws may be passed to hold my variable condenser to some suitable support. The bottom insulating cover plate 4 is held in positionby means of tacks 51, which pass through apertures in the cover plate and int-o the support members 47 and 48.

In operation, the operating knob 41 is rtated to cause the arm 28 to move the presser foot 33 into varying positions of Contact with the flexible resilient condenser element 21. By reason of the fact that the fixed element 5 and the flexible element 21 are made of curved conformation, in the present instance in the form of an arc, maximum variation in length of resistance, and hence change in resistance, can be effected within an apparatus comprising small cubic content. The

gradations of change inresistance can be made extremely small. As the arm 28 is moved to cause the presser foot 33 to bring into contact the flexible element 31 with varying lengths of the fixed resistor `5, varying portions of the resistor 5 areshort circuited by the flexible metallic element 21.

minals of the fixed resistance element, allin the same container, provides a construction of peculiar utility in connection with the use of the device as an instrument in radio communication.

By reason of the fact that the flexible spring like element 21 is intentioned away from the fixed element, there is no danger of.y

obtaining a greater degree of short-circuiting of the fixed element than is effected by actual adjust-ment of the device.

While I have shown and described the preferred embodiment of my invention, I wish it to be understood that do not confine myself to the precise details of construction herein set forth by way of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, without departing from the spirit of the invention, or exceeding the scope of the appended claims.`

I claim:

1. A variable resistance comprising a fixed element, a flexible movable element, a shaft, an arm moving-with the shaft, and a presser foot universally mounted on said arm and contacting with the surface of the flexible element to press it against the fixed element.

2. A variable resistance comprising a fixed element., a flexible movable element, a shaft, an arm vmoving with the shaft, and a presser foot loosely mounted on said arm and capable of universal movement there1n contacting with the surface of the flexible element to press it against the fixed element.

In testimony whereof I affix my signature.

HARRY R. VAN DEVENTER 

